
As this equation illustrates, the additional terms in the weak formulation only affect the mass matrix. The added matrix \(\mathbf {M}_\Gamma \)  is symmetric positive semidefinite and serves to suppress the highest eigenvalues [1]}, [2]}. The variational consistency of the added terms ensures that the true solution also satisfies FEM, which is an important property for ensuring optimal convergence [3]}, [4]}.
